To talk about sleep training, we're generally referring to some system where a child is crying for some period of time during the night and with the intention that they fall asleep on their own. So people sometimes call this "cry it out." There's a method called "verberizing," which is named after a guy named Verber.

And there are many different variants on this, but the basic core item is that the baby is crying, you are not going in to help the baby, and they eventually learn to fall asleep on their own. It's extremely polarizing because people worry that if you sleep train your kid, it will cause them to never be attached to you and to have long-term psychological issues.

We have a fair amount of evidence on sleep training. We can see that it does improve sleep. It does actually improve parents' sleep, decreases postpartum depression. And then when you look at long-term outcomes, either long-term or short-term outcomes, for kids, you just don't see any differences. For kids who are sleep trained and not, there's just not any evidence in the data of this kind of attachment issues.